fix: preserve z-indexed subplots during relayout for correct pan/zoom

[ryan-williams]

Summary

Fixes a bug where pan/zoom fails on the first interaction when traces have different zorder values. On first drag, one trace moves with the grid while the other stays frozen in place. The second pan (and all subsequent pans) work correctly — both traces move together as expected. This is particularly noticeable in react-plotly.js, which calls Plotly.Plots.resize() after mount.

Root cause: When relayout is called (e.g., during resize), supplyDefaults resets _plots via linkSubplots, losing z-indexed subplots (e.g., xyz2, xyz3). Since relayout doesn't trigger drawFramework, they aren't recreated, causing updateSubplots in dragbox.js to miss them during pan/zoom.

Fix:

• In linkSubplots (plots.js): preserve z-indexed subplots from oldSubplots
• In updateSubplots (dragbox.js): include z-indexed subplots from _plots

Demo

bug.mp4

Live before/after comparison: https://runsascoded.github.io/plotly.js/

To reproduce the bug:

1. Open the Before Fix demo
2. Drag the chart to pan horizontally
3. First drag: one trace (blue) moves with the grid, but the other trace (red) stays frozen
4. Release and drag again
5. Second drag: both traces move correctly together
6. Compare with After Fix — first drag works correctly

Test plan

• Existing cartesian_interact tests pass
• Manual testing with react-plotly.js confirms fix
• CI tests

🤖 Generated with Claude Code

[camdecoster]

I prodded Claude to dig into this and this is the resulting solution. Updating this one file should take care of the issue without updating dragbox.js. Could you give this change a shot and let me know if it fixes your problem?

Suggested change

	// Preserve z-indexed subplots (e.g. 'xyz2', 'xyz3') from oldSubplots to _plots only.
	// These are created by drawFramework when traces have different zorder values.
	// We preserve them to _plots (not _subplots.cartesian) so that drag/pan operations
	// in dragbox.js can still transform them during relayout operations that don't
	// trigger a full redraw (e.g., resize). If drawFramework runs later, it will
	// properly update/remove these subplots as needed.
	var zindexSeparator = cartesianConstants.zindexSeparator;
	for(var oldId in oldSubplots) {
	if(oldId.indexOf(zindexSeparator) !== -1 && !newSubplots[oldId]) {
	newSubplots[oldId] = oldSubplots[oldId];
	}
	}
	// Preserve z-indexed subplots (e.g. 'xyz2', 'xyz3') created by drawFramework.
	// These aren't in newSubplotList.cartesian because supplyTraceDefaults only
	// registers base subplot IDs. We restore them from oldSubplots so they
	// survive relayout cycles that don't trigger drawFramework.
	for (const [oldId, oldPlot] of Object.entries(oldSubplots)) {
	if (oldId.includes(zindexSeparator) && !newSubplots[oldId]) {
	const baseId = oldId.split(zindexSeparator)[0];
	const basePlotinfo = newSubplots[baseId];
	if (basePlotinfo) {
	// Update axis refs to avoid stale references
	oldPlot.xaxis = basePlotinfo.xaxis;
	oldPlot.yaxis = basePlotinfo.yaxis;
	oldPlot._hasClipOnAxisFalse = basePlotinfo._hasClipOnAxisFalse;
	newSubplots[oldId] = oldPlot;
	newSubplotList.cartesian.push(oldId);
	}
	}
	}

[camdecoster]

Suggested change

	var cartesianConstants = require('./cartesian/constants');
	const { zindexSeparator } = require('./cartesian/constants');

[camdecoster]

The file can remain unchanged if you follow the suggestion in plots.js.